I had an install of Debian that would not boot anymore so I went through the following steps to reinstall GRUB
I didn’t have a live CD of Debian so I used Linux Mint however the steps should be similar in Debian

  • Boot Live CD
  • Open Gparted
  • Right click each partition and run a check
  • Open the terminal window and run the following commands:
    • sudo add-apt-repository ppa:yannubuntu/boot-repair
    • sudo apt-get update
  • Open Application manager and search for Boot Repair and install
  • Launch boot repair and let it scan your partitions
  • Click Advanced Options and you can verify what it is going to do then click Apply

The above worked for me on one disk but failed on another disk so if the above fails try this:

  • Boot the disc of the distro you are trying to repair (for me it was Debian Buster)
  • Select Advanced Options
  • Select Rescue Mode
  • Click next till you get asked what partition you want to shell to
  • I selected the partition that had my data (/dev/sda2)
  • I then selected Reinstall GRUB (this is from memory)
  • When it asked for the device location I entered the main HDD (/dev/sda)
  • After install remove the CD and reboot